There is a particular desire for motors for use in compressors, electric cars, hybrid cars, fuel cell-powered cars, and the like to produce high torque, among the demands for motors to be small, light-weight, high-output, low-vibration, low-noise, and high-efficient.
In response to the above demand, there has conventionally been proposed a motor 101 as shown in FIG. 18 (see Patent Literature 1). The motor 101 includes an annular stator 102 that includes stator cores 103, permanent magnets 104, and coils 105, and a rotor 108 having a plurality of salient poles 109 (five salient poles in FIG. 18). The stator cores 103 have a plurality of teeth 110 (six teeth in FIG. 18) and an annular stator yoke 107 surrounding the outer side of each of the teeth 110. The motor 101 improves torque with use of magnetic fluxes generated by the permanent magnets 104.
However, this structure of the motor 101 has a problem. In the center of each of the teeth 110 in the circumferential direction thereof, a permanent magnet 104 is arranged that is magnetized in the circumferential direction of the stator 102. This results in that magnetic circuits arising from the N pole and returning to the S pole is shorted by the stator yoke 107 that is made of a material having a magnetic permeability higher than the magnetic permeability of air. Accordingly, most of magnetic fluxes generated by the N pole of the permanent magnet 104 return to the S pole of the permanent magnet 104 through the stator yoke 107 made of a material having a high magnetic permeability. This reduces magnetic fluxes to be flowed to the rotor 108, and as a result cannot sufficiently improve torque to be produced by the rotor 108.
In consideration of this problem, there has conventionally been proposed a motor having the structure where a magnetic circuit that arises from the N pole of each permanent magnet and returns to the S pole of the permanent magnet is broken on the way.